In order to remove toxic substances that are contained in air supplied for personnel it is first necessary to identify these substances, in order that signals and/or manipulated variables can be generated so that filtering processes and/or ventilation systems can be either activated or shut down.
It has already been proposed that analytical devices be provided in order to detect toxic substances in the air; however, such devices are comparatively costly from the point of view of acquisition and operation, quite apart from the fact that they can only determine individual components of toxic substances.
Semiconductor-based sensors can also be used for this purpose, and generally speaking these fulfill the demand that they respond to the usual contaminants present in the air. However, with respect to their response sensitivity, the operating ranges of such sensors lie significantly above the concentration levels of many toxic substances which can be toxic to humans. Furthermore, semiconductor-based sensors are sensitive to temperature variations and different flow velocities of the air currents that are to be monitored. In addition, the response times of such sensors--particularly in the range of low concentrations--and their decontamination times are too high to permit them to be used, for example, to control filter systems and/or ventilation systems in a motor-vehicle cab.